The purpose of this paper is to estimate the stability of an unburied offshore pipeline resting on a calcareous sand under severe storm condition. Pore pressure accumulation and pipeline movement during cyclic loading of pipeline have been numerically investigated from a view point of a non-linear relationship between pipeline and seabed. Both drag and lift forces acting on the pipeline are evaluated for 100 years return period storm condition using the Fourier decomposition method. Pipeline movement during cyclic loading greatly depends on the stiffness of non-linear spring element, and pore water pressure response as well as shear strain are more sensitive to the initial unit tangential stiffness of non-linear spring element.